Known suspension systems including a roll control device, and controls of the suspension systems are described in JPH05 (1993)-50819A, JPH05 (1993)-16633A, JPH04 (1992)-166408A. According to the known suspension systems including the roll control device, a control value of the roll control device is determined using actual lateral acceleration which is actually generated lateral acceleration at a vehicle body, and estimated lateral acceleration which is estimated on the basis of vehicle traveling speed and a degree of steering.
According to the known suspension systems, gains of the actual lateral acceleration and the estimated lateral acceleration are varied on the basis of vehicle traveling speed and steering speed, or the like, for determining the control value in order to perform a control based on the estimated lateral acceleration in addition to a control based on the actual lateral acceleration in view of delay of control at initial stage of turning movement of the vehicle, swing back when returning a steering operation member, and excessive slip during the turning movement of the vehicle, or the like. Lateral acceleration is generated not only when a vehicle is turning, but also when a vehicle travels on a rough road even if the vehicle travels straight. Thus, it is desired to avoid the influence of the lateral acceleration when controlling the roll control device. With the foregoing known suspension systems, the aforementioned influence of the lateral acceleration is not considered, and in a practical use, the known suspension systems leave room for improvement.
A need thus exists for a suspension system for a vehicle including a roll control device, which can avoid influence of relatively small degree of lateral acceleration which is not caused by turning movement of the vehicle.